1. Field of the Invention
This invention relates to magnetic recording mediums in the form of tapes and disks.
2. Description of the Prior Art
Magnetic recording mediums for use in audio apparatus, video tape recorders and computers show a growing tendency toward higher density. For recording, a high frequency signal is frequently being used. Accordingly, there is a problem that a loss of spacing between a magnetic head and a magnetic recording medium greatly influences the output signal.
In order to reduce the spacing loss, there has been proposed a magnetic recording medium whose magnetic layer is made as smooth or flat as possible.
However, if the surface of the magnetic layer is very flat, the coefficient of friction increases, thus tending to cause the tape winding on a reel to be disarranged. When a tension on the tape varies, a stick-slip phenomenon is liable to take place. Although smooth recording and reproducing operations are ensured, the magnetic tape suffers defects from contact with guide members and flanges of a recording and reproducing apparatus.
In order to overcome the drawbacks, an attempt has been made to make a rough surface on one side of a non-magnetic support which is opposite to a magnetic layer-bearing side. In such a attempt, the rough surface is provided to reduce the coefficient of friction. However, when a magnetic recording medium whose back surface is rough is wound, the irregularities on the rough surface are transferred to the magnetic layer, thereby forming irregularities on the magnetic layer surface. This invites an increasing loss of spacing mentioned above, bringing about a lowering of output.
Another attempt has been made to form a back coat layer on one side of a non-magnetic support in order to reduce the coefficient of friction. In the back coat layer, there are used carbon black and lubricants. However, a mere combination of carbon black and lubricants is disadvantageous in that the surface smoothness is poor, a coefficient of dynamic friction is so large that the travelling performance is not good, and dispersability of carbon black is relatively poor.